This invention relates generally to speakers and more particularly to a sub-woofer speaker having a gas impermeable suspension system that operates in conjunction with directed air flow channels for cooling of the voice coil.
Conventional speakers have a support frame, a voice coil, an upper suspension for support of a cone, a lower suspension system xe2x80x9cspiderxe2x80x9d for support of a voice coil, and a motor structure that drives the voice coil. The motor structure is typically a permanent magnet mounted to a back plate of the support frame with a pole piece extending into the center of the voice coil. The voice coil has a winding of wire that converts electrical energy supplied to axially movement of the voice coil, relative to the pole piece. Movement of the voice coil creates audible sound.
A problem with high output speakers, such as sub-woofers, is that the voice coil becomes super heated during operation. The voice coil in a conventional suspension system is support by a resin treated cloth material, commonly referred to as the spider. The cloth material allows for the transfer of air through the material providing for cooling of the voice coil. The spider is attached to the voice coil by an adhesive which, over time and/or during high temperature use, becomes weak due to voice coil heat. If the adhesive is breached, sound reproduction is reduced or lost completely. The prior art attempts to provide a spider that allows heat transfer while maintaining flexibility. A problem with the conventional spider is that the attachment surface is very thin which can quickly affect adhesive life. The inner diameter of the spider forms provides the entire surface for the adhesive attachment, the surface area is typically no greater in width than the thickness of the spider.
The driver motor of a speaker is constructed of a winding of copper or aluminum wire about a former to form the voice coil. The voice coil is suspended within a magnetic field formed by the combination of a front plate, a magnet and a pole piece attached to a backplate. When an electrical current is applied to the winding, the speaker cone vibrates according to the audio frequency and polarity of the applied signal. The electrical resistance of the voice coil to current flow generates the heat and therefore increases the temperature within the speaker. This resistance to current flow represents a significant part of the driver motor""s impedance, and a substantial portion of the electrical input power is converted into heat rather than into acoustic energy. In high power sub-woofer driver situations, it is common for the voice coil to reach temperatures ranging over 500xc2x0 F. The ability of the speaker to tolerate heat is impacted by the attachment point of the spider where the adhesive is employed, as well as suspension excursions which place alternating stresses on the spider. The operation and performance of a speaker system is therefore inherently limited by its ability to tolerate and dissipate heat.
The use of a vented pole piece assists in the exhaust of heated air from the inner area and eliminates the audible noise typically found in non-vented pole pieces. The vented pole piece increases the thermal resistance of the sink thereby lowering the power handling capability of the speaker and is generally accepted as the preferred speaker embodiment due to the need for cooling the voice coil. Various attempts at glue enhancements have also been attempted but cannot address the numerous variables including consumer operation, speaker placement, age and UV deterioration.
A variety of designs have been employed in an attempt to address the problems associated with heat build up in speakers. Much of the design effort has been developed to creating a flow of cooling air over the voice coil itself, such as disclosed, for example, in U.S. Pat. No. 5,042,072 to Button; U.S. Pat. No. 5,081,684 to House; and U.S. Pat. No. 5,357,586 to Nordschow et al. A typical construction in speaker designs of this type involves the formation of passages in or along the voice coil which form a flow path for the transfer of cooling air from the cavity between the voice coil and the dust cap and/or diaphragm, and vent openings usually formed in the back plate of the motor structure. An air flow through these passages is created in response to movement of the diaphragm moves in one direction, air is drawn from outside of the speaker, through the vent opening in the back plate, along the passages in or along the voice coil and then into the cavity. Movement of the diaphragm in the opposite direction creates a flow out of the cavity along the reverse flow path. A problem with the approach described above is that the design and construction of the flow passages often do little more than provide venting of the area since the actual air flow generated by movement of the spider is typically relatively low volume. As a result, very little cooler ambient air from outside of the speaker actually flows along the voice coil to provide effective cooling.
U.S. Pat. No. 5,042,072 discloses an attempt at making a self-pumping action to create a flow of air through ventilating paths which, in turn, lower the temperature of the voice coil. The magnetic structure or pole piece has channels whereby cool air may be introduced and hot air may be exhausted to cool a voice coil by movement of the speaker diaphragm. The flow passages do little more than provide venting of the area or cavity between the dust cap and the voice coil. The flow generated by movement of the spider is typically relatively low volume as the spider is designed to allow air passage to assist in the cooling. As a result, very little cooler ambient air from outside of the speaker actually flows along the voice coil.
U.S. Pat. No. 4,757,547 discloses an external blower which forces air over the voice coils to cool them. However, in practice this system has drawbacks. As the gap between the voice coil and the pole piece of the magnet is very small (approximately 0.010 inches) cooling can only be achieved by forcing air through this air gap at a very high air pressure. Under a high air pressure, the dome will take on a positive set and cause the coil to be no longer centered in the gap. This offset will cause second-harmonic distortion. Additionally, the blower can be loud and obviously non-musical, resulting in speaker distortion and excessive noise.
It is a well known in the art to utilize additional components to prevent significant temperature rise in the voice coil. For example, a metallic voice-coil bobbin is often used to conduct heat way from the region of the voice coil. As another example, the voice coil is often coated with a low viscosity fluid to transfer heat produced by the voice coil into the magnetic structure from which it can more easily radiate into the surroundings. As yet another example, heat radiating fins are often mounted on the permanent magnet to improve secondary cooling.
The use of additional components to prevent significant temperature rise in the voice coil introduces numerous drawbacks. In particular, the use of additional components significantly increases the complexity of the speaker and consequently increases the overall cost of the speaker.
U.S. Pat. No. 5,357,586 to D. D. Nordschow discloses a flow-through air-cooled loudspeaker system. The loudspeaker and enclosure are provided with aerodynamically-shaped passages providing low-pressure regions for inducing flows of air into and about the driver motor of the loudspeaker in response to vibratory movement of the speaker cone. An aerodynamically-shaped body is disposed within the pole piece to define a venturi passage for exchange of air between an interior chamber defined by a coil former and the back of the speaker. Aerodynamically shaped openings are provided through the pole piece for inducing flow of air about the voice coil in the voice coil gap between the pole piece and permanent magnet. The speaker frame support is provided with aerodynamically-shaped openings to induce air flow into the interior chamber. In this manner, low-pressure regions established by the aerodynamic shapes induce flow of cooling air about the voice coil and pole piece in response to vibratory movement of the speaker.
In U.S. Pat. No. 5,909,015 to Yamamoto, there is disclosed as loudspeaker that is cooled by drawing air through a side intake aperture and exhausting the air through the center of the voice coil. However, the volume of air drawn around the voice coil and into the dusk cap and result in distortion when high energy levels are employed. Speakers which utilize venting techniques typically experience venting difficulty in drawing cooler air, and passing out warmer air since the spider is used as the ventilating pump. The conventional spider does not have the ability to pump air, while allowing the passage of air.
Thus, what is needed in the art is a means for cooling the voice coil that does not add additional components to the system but allows for a high volume of air to be pumped across the voice coil.
In general the instant invention is a high output sub-woofer speaker having air intake and exhaust apertures, and a voice coil supported by a diaphragm constructed of gas impermeable material. The impermeable material, preferably rubber can be made thicker than conventional resin coated cloth spiders thereby providing a large adhesive attachment point. Operation of the voice coil causes the diaphragm to draw air through the air intake apertures where it is drawn past the voice coil and vented out through the exhaust apertures. The diaphragm operates as an air pump forcing the air past the voice coil for supplying of cool are and exhausting of heated air. A unidirectional flap may be used on the vented frame to an create air flow current past the voice coil for higher efficiency. The diaphragm allows for elongation of the suspension system with the damage found to over driven cloth suspension systems. Further, the air pump diaphragm provides longevity to the adhesive which joins the voice coil to the diaphragm by removing of heat that would otherwise compromise the adhesive.
Thus, an objective of the invention is to provide cooling of the voice coil and associated voice coil adhesive connection.
Another objective of the invention is to provide a suspension system that has a primary function to operate as an air pump for drawing air past the voice coil, and a secondary function to act as a support for the voice coil.
Still another objective of the invention is to provide enhanced cooling of the voice coil by directing a cool air intake at the voice coil as compared to allowing air to circulate in the space under the spider or dust cap.
Yet still another objective of the invention is to mount a disk between the frame and the front plate, or modify the front plate, having radial cut channels for directed placement of air around the voice coil.
Still another objective of the invention is to employ the use of a vented frame with a unidirectional aperture for exhausting of heated air.
Still another objective of the invention is to disclose a spider replacement that has a predictable and equal throw in both the positive and negative excursions.
An advantage of the instant invention is to provide a suspension system that can handle higher positive and negative excursions without damage.
Another advantage of the presented suspension system is the enhanced surface area made possible between the voice coil and the diaphragm allowing for greater adhesive attachment.
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.